Examples of currently-used nuclear medicine diagnosis apparatus include a PET (positron emission tomography) apparatus. The PET apparatus reconstructs a tomographic image of a subject only when a plurality of detectors detects two beams of γ-rays coincidently generated due to annihilation of positive electrons (positrons). Moreover, examples of the PET apparatus include a mammography PET apparatus that images the breast of the subject. The mammography PET apparatus includes detectors that surround the breast of the subject. The detectors are disposed closely to the breast of the subject, enhancing detection sensitivity.
The γ-rays detected with the detectors are γ-rays emitted from the inside of the subject to which the radiopharmaceutical is administered in advance. The emitted γ-rays are absorbed in tissue within the subject. Consequently, the PET apparatus performs absorption correction taking into consideration of influences of γ-ray absorption upon generating a PET image (see, for example, Patent Literature 1). The absorption correction is typically performed with data upon imaging with an X-ray CT apparatus and data upon detection with an external source that emits γ-rays. However, it is difficult to provide the X-ray CT apparatus or the external source on the mammography PET apparatus. Accordingly, absorption correction is performed under assumption that the breast of the subject is a single absorber. In this method, a contour of the breast is extracted, and an absorption coefficient equal to that of the breast is assigned in the extracted contour, whereby an absorption coefficient map is generated. Then, the absorption correction is performed based on the generated absorption coefficient map.
A dynamic contour model such as a level set method is used as the method for extracting a contour of an object such as the subject (see, for example, Non-Patent Literature 1). The dynamic contour model is a method of extracting the contour by dynamically changing a closed curve on the image to conform to the contour of the object.
Patent Literature 1: Japanese Unexamined Patent Publication No. 2003-294843A
Non-Patent Literature 1: C. Li, C. Xu, C. Gui, and M. D. Fox, “Level Set Evolution Without Re-initialization: A New Variational Formulation”, CVPR 2005